**THIS DOES NOT COVER EVERYTHING**Fluid Mechanics Year 1 Civil Engineering definitions:A Fluid is a substance that deforms continuously under the application of a shear stress.Viscosity is a measure of how much resistance a fluid has to shearPressure:

Absolute: Pressure with respect to vacuumGauge: measured relative to local atmospheric pressure

The buoyancy force: If a body is immersed in water, the hydrostatic pressure distribution causes a net upward buoyancy force equal to the weight of the displaced fluid.Steady Flow: Flow does not change with timeStreamline: A line that is everywhere tangential to the instantaneous flow velocity.Ideal fluid: experiences only normal stresses.Real fluid: Do have viscosity, which generate shear forces.Boundary Layer: A flow region where large differences in velocity occur (large velocity gradients); this is often very close to the wall.Viscosity: A measure of how much resistance a fluid has to shear.

τ=μdudz

Reynolds number ℜ=ULν

( inertiaviscosity ) Expresses the ratio between

inertial and viscous forces ( ℜ=URν

in open channels, turbulent

>>500)Lagrarian approach: small elements (‘particles’) of fluid within the flow followed for all timeEulerian approach: A CV is drawn around a fluid system and the flow into/out-of surfaces are considered.

Unsteady continuity equation: Q1−Q2=dVdt

Momentum conservation: Assume flow in x-direction onlyThe steady Bernoulli equation: E= constant along streamline where

E=p+ρgz+ 12ρU 2

. Assuming steady flow, constant density flow, no

friction.2nd Bernoulli eq’n: pressure across straight streamlines is constant.Bernoulli is valid: converging streamlines, fluid accelerating, no energy losses.Venturi tube: device for determining the volume flux Q(or U) in a pipe.

Open Channel Flow: A conduit through which liquid flows with a free surface and this flow is driven by gravity.

hm=Aw, R= A

PFroude Number: the ratio of the mean flow velocity U and the shallow-water wave velocityGravity balances Friction:

Fg , x=mgsinθ=ρ gALsinθ≈ ρgALs F f=τwPL=¿ τw= ρ gRS

Chezy: U=C√Rs. For turbulent flow: τ w=c f ρU2=> U=√ gRsc f

Chezy used C=√ gc f

. (rough)40 <C< 80(very smooth)

Froude similarity FrM=Fr P scale ratio √ λHydraulic Jump -> use momentum conservation (and divide by h1

3, solve quadratic -> Belanger equation)

Sluice gate -> eliminate h2−h1 introducing α= Q2

2g w2Bernoulli

Restriction in channel width: Results in reduced water level as velocity head is increased. Piezometric head decreases so that E remains constant.